(a) Field of the Invention
The present invention relates to a device and method for detecting a cyclic prefix length.
(b) Description of the Related Art
A communication system in an orthogonal frequency division multiplexing (OFDM) scheme divides all channels into narrowband sub-channels having a orthogonality and transmits them, thereby making it possible to effectively overcome selective fading of a frequency. The OFDM scheme inserts a cyclic prefix with a longer period than a delay spread of a channel into a front end of a symbol to maintain the orthogonality of the symbol, thereby making it possible to remove inter-symbol interference (ISI). As a result, the OFDM scheme is effective in high-rate data transmission.
However, the advantage of the OFDM scheme is possible only when the inter-subcarrier orthogonality is maintained. Therefore, when the orthogonality is broken, adjacent inter-channel interference (ICI) occurs, thereby deteriorating system performance. Therefore, in the system in the OFDM scheme, time and frequency synchronization of the receiving apparatus are important.
Meanwhile, a receiving apparatus such as a mobile station, etc., performs timing synchronization of an OFDM signal by using a preamble signal transmitted by the base station. Generally, the preamble includes an active symbol having a predetermined fast Fourier transform (FFT) size and a cyclic prefix that is inserted in front of the active symbol. The cyclic prefix is the same as a signal of the last period of the active symbol.
The receiving apparatus receives the preamble from the transmitting apparatus, and should accurately know a start position of a signal in order to demodulate the signal using the fast Fourier transform (FFT).
Meanwhile, in the OFDM-based communication system, the downlink preamble is used in initial synchronization, frequency offset, and cell search, and has a structure in which a pattern in a time domain is repeated by a predetermined frequency and is symmetrical, after an inverse fast Fourier transform (IFFT).
The OFDM signal supports various cyclic prefix lengths according to the condition where the system is applied. Therefore, the mobile station receiving the downlink should detect the cyclic prefix length that is used in the base station to transmit and receive the signal.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.